An alcohol fuel such as ethyl alcohol, a benzine fuel of the petroleum benzin type including gasoline or a liquid gas fuel such as butane gas or propane gas is generally used as the fuel of a cigarette lighter, fire-lighting device, torch, lamp or other such burner.
The performance, ease of use, and structural design of such burners differs depending on the kind of fuel used, and each has its own characteristics.
In the case of a benzine fuel that is a mixture of petroleum benzin-type hydrocarbon compounds, for example, the fuel is a mixture of compounds with different boiling points. After the burner is lit, volatilization of the components begins with the low-boiling-point benzine components and then progressively shifts to hydrocarbons with higher boiling points. Since the composition of the fuel remaining in the burner therefore varies over the burning period, the flame length changes. The same is true of gasoline. As benzine and gasoline have high volatility, burners that use them require a sealed structure for reducing evaporation from the fuel storage section and the wick portion. If the sealing is insufficient, fuel is lost through evaporation and the frequency of bothersome fuel refills increases. In addition, benzine and gasoline have distinctive odors which may be found disagreeable.
In the case of a liquid gas fuel, the gas pressure is high in the use temperature range of the burner and the vessel storing the fuel has to have a pressure-resistant structure. Moreover, the flame length changes with variation in the gas pressure and since it is a characteristic of the gas pressure to vary logarithmically and greatly with temperature, large change in flame length with temperature becomes a particular problem. In order to reduce this flame-length variation, the fuel supply system of the burner requires a special design countermeasure for effecting temperature compensation, which complicates the structure and is disadvantageous from the aspect of cost.
As regards an alcohol fuel, on the other hand, a liquid fuel composed mainly of alcohol, e.g., a lower monovalent alcohol such as methyl alcohol, ethyl alcohol or propyl alcohol, is a liquid at ordinary temperatures and is also relatively low in vapor pressure. The fuel storage section therefore does not require a pressure-resistant vessel and the sealing structure for sealing the fuel tank and the wick need only be capable of preventing alcohol evaporation. This is advantageous from the point of simplifying the structure and lowering the cost of the burner.
Further, in the burner using a liquid fuel composed mainly of alcohol, the means used to supply the liquid fuel from the fuel storage section to the flame-producing section is generally a wick that, utilizes the surface tension of the liquid fuel to draw it up through continuous fine holes or fine voids among bundled thin fibers by capillarity and burns it at the tip portion thereof.
Specifically, the wick used for drawing up the fuel is a string-like one obtained by twisting fibers, one obtained by bundling glass fibers, one using both of these with the glass fibers enclosed in cotton yarn and the result wound with fine metal wires to prevent disintegration, or the like, whose lower draw-up section functions to draw up fuel to be burned at the upper flame-producing section.
In the burner using a wick of the foregoing type, moreover, the initial flame length after lighting, the change in flame length, the saturated flame length and the like differ depending on the material, size and shape of the wick. The burner must therefore be configured to provide the desired characteristics.
In the case of a cigarette lighter or other burner fabricated to use a liquid fuel composed mainly of alcohol, fuel present on the wick surface starts to burn and form a flame after the wick is lit. The length of this flame will be called the initial flame length.
This wick is then heated as the burning continues. As the amount of fuel vaporized from the surface of the wick therefore increases, the flame grows longer. As the burning proceeds, however, the temperature rise produced by the burning of fuel on the wick reaches a state of equilibrium and stops. The growth of the flame length also saturates and stops at the saturated flame length. As the fuel burns/vaporizes from the surface of the wick, fuel disperses from the interior of the wick to the surface thereof and is replenished by fuel drawn up from the fuel tank through the draw-up section of the wick.
When fuel is consumed from the wick surface, fuel is supplied from the wick interior and fuel is drawn up and supplied from the fuel tank, the fuel stays in a state of equilibrium and the flame length stabilizes. If the consumption of fuel from the surface of the wick is not accompanied by a corresponding supply of fuel from the wick interior, the flame length changes from the initial flame length and the state of equilibrium with the fuel supply is lost.
In a cigarette lighter, fire-lighting device or other such burner, the burning conditions that must be satisfied are that the initial flame length immediately after lighting be maximized, a practical length being at least around 20 mm, that the time for the flame length to reach 25 mm be minimized, i.e., be made not more than 10 seconds from the practical viewpoint, and that the saturated flame length with passage of time after lighting be kept from becoming too long, i.e., be kept to around 70 mm from the practical viewpoint.
To achieve these conditions with a wick of circular cross section, however, the amount of projection of the wick from the wick holder has to be made large if the outer diameter of the wick is made small, while if the amount of projection is to be reduced, the outer diameter has to be made large. In either case, the structure is difficult to make compact because of considerations relating to the size and opening/closing operation of the closure cap for preventing evaporation of fuel from such a wick. The preferred structure is one that minimizes both the size of the wick and the amount of wick projection.
In view of the foregoing circumstances, the present invention is aimed at providing a wick for a liquid fuel burner, particularly a burner that uses a liquid fuel composed mainly of alcohol and that enables minimal wick projection amount and compact configuration while ensuring optimum burning conditions.